Adults with Attention Deficit Hyperactivity Disorder (ADHD) have impairments in attentional subsystems of alerting and conflict monitoring. Mindfulness meditation may lead to an improvement of these deficits, and reduces symptoms of anxiety and depression. However, the studies that demonstrated these improvements did not use a control group, nor controlled the use of medication. In the present study the investigators will examine the effects of the mindfulness practices (same protocol of 8 weekly sessions used in the study that showed positive effects in this disorder) in the performance of adult patients and healthy people (with ADHD). Cognitive performance, mood, and the quality of life will be assessed by validated questionnaires before and after treatment/standby.